Tear resistant multilayer films and articles incorporating such films

ABSTRACT

A tear resistant film comprises more than five layers situated one on the other in a parallel array. The layers are individually selected from a stiff polyester or copolyester, a ductile polymeric material, and optionally, an intermediate material. The stiff polyester or copolyester is oriented in at least one direction. Tear resistance may be measured in a Graves area test and reflects the ability of the film to absorb energy. The films of the invention are useful in many articles including security control laminates for glazing members.

This is a continuation of application No. 07/955,357 filed Oct. 1, 1992,now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to multilayer films, and, more particularly, totear resistant multilayer films comprising alternating layers ofrelatively stiff and ductile polymeric materials.

2. Description of the Related Art

Traditionally, "tear resistance" has described the ability of a film toresist continuing to tear once a tear has been started. Trash andgrocery bags, often based on polyolefins such as polyethylene, areexamples of films that are conventionally considered to be tearresistant. These films have considerable stretch which enables them toresist advancing an already formed tear. By "stretch" it is meant thatthe films have a low tensile modulus and are not dimensionally stable.

Also known are films which are relatively stiff In this regard, "stiff"refers to films which cannot be stretched significantly withoutbreaking; that is, films which are dimensionally stable, creep-resistant(stretch resistant), and of high modulus. Examples of stiff,dimensionally stable, high modulus materials are certain packaging filmssuch as cellophane, polyesters and biaxially oriented polypropylene.However, these films have low tear resistance. That is, once a tear hasbeen started, the film continues to tear quite easily.

There are numerous applications where stiff, tear resistant films wouldbe desirable. For example, films which provide sign faces and buildingawnings must be tear resistant to have a useful life. On the other hand,these films must also be relatively stiff so that they will not billowin the wind or sag with age.

Backings for abrasive sanding belts experience harsh operatingconditions and must resist tearing. However, sanding belts which stretchare undesirable because they may not fit securely on the sander and maywork free under normal use.

Angioplasty balloons for expanding blood vessels during surgery requirestiff, tear resistant films. The balloons cannot readily shatter (i.e.,tear) during use. The balloons must also inflate to a controlled sizeand should not stretch to a larger size.

For certain tapes, stiff, tear resistant backings would be desirable.Such backings would not readily continue to tear if inadvertently nickedor cut when dispensed. At the same time, the backings would be stretchresistant which could enhance the stability of articles taped therewith.

Films for shatterproofing windows need to be tear resistant. However,the performance of such films would be enhanced if the films were alsostiff and tear resistant as the combination of these properties wouldhelp the film to absorb energy in the event of a window shatteringimpact.

Numerous packaging films are disclosed in the prior art. U.S. Pat. No.3,188,265, "Packaging Films" issued Jun. 8, 1965 to R. Charbonneau, etal. discloses a heat-sealable film comprising polyethylene extruded ontoa web of oriented polyethylene terephthalate. U.S. Pat. No. 4,705,707"Polyethylene/Polyester Non Oriented Heat Sealable, Moisture BarrierFilm and Bag," issued Nov. 10, 1987 to J. Winter discloses a moisturebarrier film useful in microwaveable food pouches. The film comprisesthree and five layer nonoriented structures of polyethylenes andpolyesters or copolyesters.

U.S. Pat. No. 4,965,108 "Low Temperature Impact and Puncture ResistantThermoplastic Films and Bags Therefrom," issued Oct. 23, 1990 to E. Bielet al. discloses multilayer film and bag structures comprising apolypropylene copolymer inner layer, an outer layer (e.g., a polyesteror a polyamide), and a polypropylene based bonding resin therebetween.

U.S. Pat. No. 4,636,442 "Laminated Structures of PolyethyleneTerephthalate and Elastomeric Copolyesterethers," issued Jan. 13, 1987,to R. Beavers et al. discloses multilayer films reportedly havingimproved flex-crack resistance. The films are based on polyethyleneterephthalate and elastomeric copolyesterethers. Biaxially orientedthree and five layer films in which the amount of copolyesterether isfrom about 5 to about 75 weight % (preferably 10 to 60 weight %) aredisclosed.

U.S. Pat. No. 4,939,009 "Multilayer Sheets Having Excellent Adhesion,"issued Jul. 3, 1990, also to R. Beavers et al., discloses three and fivelayer films based on polyolefins and copolyesterethers with tie layerstherebetween.

U.S. Pat. No. 4,729,927 "Polyester Packaging Material," issued Mar. 8,1988, to M. Hirose et al. discloses a packaging material comprisingpolyethylene terephthalate and a second material based on polyethyleneisophthalate copolymerized with an aliphatic hydroxycarboxylic acidhaving up to eight carbon atoms. Reportedly, the number of layers is notparticularly critical, although films with up to five layers are said tobe preferred.

Japanese Kokai Patent No. 2-270553 "Multilayer Plastic Sheet with GasBarrier Feature," published Nov. 5, 1990 discloses multilayer filmsbased on layers of saponified ethylene/vinyl acetate copolymers,modified polyolefin adhesives, and thermoplastic polyesters.

Impact resistant and/or shatterproof security films for windows are alsoknown. For example, U.S. Pat. No. 3,899,621 "Security Film forShatter-Proofing Windows," issued Aug. 12, 1975 to M. Willdorf disclosesthree and five layer films comprising layers of polyesters andpolyurethanes. Preferably, the polyester layers range in thickness from0.5 to 5 mils and the polyurethane layers range in thickness from 0.2 to0.4 mil. U.S. Pat. No. 3,891,486 "Process for Producing Solar ControlWindow," issued Jun. 24, 1975, also to M. Willdorf, discloses a solarcontrol film comprising a pair of polyester (e.g., polyethyleneterephthalate) layers each from 0.25 to 1 mil thick with avapor-deposited aluminum coating and an adhesive therebetween.

U.S. Pat. No. 4,945,002 "Impact-Resisting Anti-Lacerative Window Units,"issued Jul. 31, 1990 to I. Tanuma et al. discloses a three layer filmcomprising two exterior layers (e.g., an ethylene/vinyl acetatecopolymer, an ethylene/vinyl acetate/triallyl isocyanurate terpolymer, apolybutyl butyral, a polyvinylformal, or a polyurethane), and anintermediate layer (e.g. polyethylene terephthalate, polyamides,polyester polyethers, polysulfones or polyimides) therebetween. The filmis sandwiched between a pair of transparent glass or plastic plates.

Various tapes are also known. For example, U.S. Pat. No. 4,091,150"Coextruded Polyester Splicing Tape," issued May 23, 1978 to G. Roelofsdiscloses a multilayer tape comprising a support film formed from atough, flexible polyester (e.g. polyethylene naphthalate or polyethyleneterephthalate) which is coextruded with an adhesion promoting polyester.A thermoset adhesive is adherently bonded to the adhesion promotingpolyester.

U.S. Pat. No. 4,908,278 "Severable Multilayer Thermoplastic Film,"issued Mar. 13, 1990 to Bland et al. discloses a multilayer film whichmay be easily and precisely cut in a straight line. The film comprisesalternating layers of brittle and ductile materials. Japanese KokokuPatent Publication No. 63-5394 "Laminate Film," published Oct. 26, 1988,discloses three and five layer tape backing films comprising layers ofdifferent polyesters. Reportedly, the films have good manual tearingproperties.

U.S. Pat. No. 4,540,623 "Coextruded Multi-layer Articles," issued Sep.10, 1985 to J. Im et al. discloses an impact resistant multilayerlaminate comprising alternating layers (preferably at least about 40layers) of coextruded polymeric thermoplastics wherein one of thematerials contains a carbonate polymer. Suggested uses include glazingapplications for windows and signs.

European Patent Application No. 0,426,636 "Iridescent Film withThermoplastic Elastomeric Components," published May 8, 1991 discloses atransparent thermoplastic film of at least ten layers. The adjacentlayers differ in refractive index and at least one of the layers isbased on a thermoplastic elastomer resin. The layers range in thicknessfrom 30 to 500 nanometers.

SUMMARY OF THE INVENTION

In general, this invention relates to a tear resistant film comprisingmore than five layers situated one on the other in a parallel array. Thelayers occur essentially randomly in the array and are individuallyselected from a stiff polyester or copolyester and a ductile polymericmaterial. Preferably, the stiff polyester or copolyester layers areoriented in at least one direction and, more preferably, are biaxiallyoriented.

By "tear resistant" it is broadly meant that a film according to theinvention demonstrates a Graves area in one direction of the film whichexceeds the Graves area in the same direction for a single layer filmcomprising only the stiff polyester/copolyester of the multilayer film,the single layer film being processed in the same manner as and tosubstantially the same thickness as the multilayer film. Preferably,multilayer films according to the invention demonstrate a Graves area inone direction of the film equal to at least about 40+0.4(x) kpsi %wherein x is the nominal thickness of the film in microns. Morespecifically, Graves area is obtained by mathematically integrating thearea beneath the curve in a graphical plot of the stress (as measured inkpsi) experienced by the film versus the strain (as measured in Graveselongation which is defined more fully below) that the film undergoesduring a test in which a film sample specifically shaped for the Gravesarea test is clamped between opposed jaws that are moved apart at aconstant rate to concentrate the tearing stresses in a small area. Thus,Graves area is a combined measure of the film's tensile modulus (i.e.,the film's stiffness and dimensional stability) and the ability of thefilm to resist advancing a tear. Consequently, Graves area may beregarded as a measure of the total energy required to cause the film tofail; that is, the ability of the film to absorb energy.

Moreover, preferred multilayer films desirably exhibit a Graveselongation at break (defined below) of at least 20%, more preferably atleast 40% during the Graves area test. In addition, preferred multilayertear resistant films according to the invention demonstrate a tensilemodulus (as measured in a conventional tensile test) of at least 175kpsi (1,208 MPa), more preferably at least 240 kpsi (1,656 MPa), andmost preferably at least 450 kpsi (3,105 MPa) in at least one directionof the film.

Both the thickness of the film and the individual layers which comprisethe film may vary over wide limits. Films according to the inventiontypically have a nominal thickness of from about 7 to 500 μm, morepreferably, from about 15 to 185 μm. The individual layers of stiffpolyester or copolyester typically have an average nominal thickness ofat least about 0.5 μm, more preferably from greater than 0.5 μm to 75 μmand, most preferably, from about 1 to 25 μm. It is preferred that theductile material layers be thinner than the stiff material layers. Theductile material layers may range in average nominal thickness fromgreater than about 0.01 μm to less than about 5 μm, more preferably fromabout 0.2 to 3 μm.

Similarly, the exact order of the individual layers is not critical. Thetotal number of layers may also vary substantially. Preferably, the filmcomprises at least 5 layers, more preferably from greater than 5 layersto 35 layers, and most preferably 13 layers.

Stiff polyesters and copolyesters useful in the invention are typicallyhigh tensile modulus materials, preferably materials having a tensilemodulus, at the temperature of interest, greater than 200 kpsi (1,380MPa), and most preferably greater than 400 kpsi (2,760 MPa).Particularly preferred stiff polyesters and copolyesters for use infilms according to the invention comprise the reaction product of adicarboxylic acid component selected from the group consisting ofterephthalic acid, naphthalene dicarboxylic acid such as dimethyl 2,6naphthalene dicarboxylic acid, and ester derivatives thereof, and a diolcomponent selected from the group consisting of ethylene glycol and1,4-butanediol. Additional stiff copolyesters based on these materialsmay be provided by copolymerizing these ingredients with one or moreother diacids and/or one or more other diols. Ductile materials usefulin the practice of the invention generally have a tensile modulus ofless than 200 kpsi (1,380 MPa) and a tensile elongation (defined below),at the temperature of interest, of greater than 50%, preferably greaterthan 150%. The ductile polymer may be selected from, for example,ethylene copolymers, polyesters, copolyesters, polyolefins, polyamidesand polyurethanes. However, a preferred ductile polymer is a copolyestercomprising the reaction product of cyclohexane dicarboxylic acid (orester derivatives thereof), cyclohexane dimethanol andpolytetramethylene glycol.

Surprisingly, beneficial improvements in the tear resistance of filmscomprising alternating layers of stiff and ductile materials arerealized when the ductile material provides less than 5 weight % of thefilm. Ductile material amounts of at least about 1 weight % (preferablyat least about 2.6 weight %), up to about 10 to 20 weight % of the filmmay be useful.

Films according to the invention may optionally include a layer of anintermediate material disposed between otherwise adjacent layers of thestiff and ductile polymers. Useful intermediate materials may beselected from a wide variety of polymers and, in some cases, may beselected to enhance the adhesion between the otherwise adjacent stiffand ductile layers. One or more functional layers may also be applied toone or both of the major surfaces of the film.

Multilayer films according to the invention provide an improvedcombination of stiffness and tear resistance especially when compared tofilms comprising only a single layer of one of the materials or singlelayer blends of both materials. Films according to the invention areuseful in a wide variety of products, including, for example, sign facesand backings for coated abrasive articles.

The multilayer tear resistant films of the invention are particularlyuseful as security control laminates for shatter-proofing glazingmembers against impact or explosion. In one embodiment of thisapplication, the invention pertains to a security control laminatecomprising a first tear resistant film having a first face and a firstlayer of adhesive on the first face for bonding the laminate to aglazing member. Typically, the adhesive coated face of the tearresistant film is temporarily disposed on a removable release linerwhich is discarded during application of the laminate to the glazingmember. The security control laminate may further comprise means forabsorbing ultraviolet radiation such as a coating layer interposedbetween the first tear resistant film and the layer of adhesive.Security control laminates according to the invention may also comprisea dyed film (bonded to the second face of the tear resistant film) andan abrasion resistant coating on the otherwise exposed surface of thedyed film.

In other embodiments, the security control laminate may comprise asecond tear resistant film which is adhesively bonded to the first film.Such constructions may also include ultraviolet radiation absorbent andabrasion resistant coatings. Also contemplated is the inclusion of ametalized layer for imparting solar control properties to the securitycontrol laminate. A metalized layer may comprise an optically clear filmhaving a layer of aluminum, gold, silver, copper, nickel and the likethereon. The security control laminate may be applied to a singleglazing member or positioned between two glazing members. The glazingmember(s) can be mounted within a frame to which the security controllaminate may be optionally secured.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood with reference to thefollowing drawings in which similar reference numerals designate like oranalogous components throughout and in which:

FIG. 1 is an enlarged perspective view of a multilayer tear resistantfilm according to the invention;

FIG. 2 is an enlarged perspective view of the film of FIG. 1 and furthercomprising a functional layer applied to one surface thereof;

FIG. 3 is a schematic diagram of the shape of a film sample used todetermine tear resistance of multilayer films according to the inventionin a Graves area test;

FIG. 4 is a graphical representation of stress vs. Graves elongation ina Graves area test for three different films;

FIG. 5 is a graphical representation of Graves area vs. weight % ofductile material for several films according to the invention;

FIG. 6 is a graphical representation of Graves area vs. film thicknessfor several films according to the invention and several comparativefilms;

FIG. 7 is an enlarged, vertical sectional view of a glazing unitaccording to the invention which includes a security control laminatebonded to a glazing member, the laminate comprising two multilayer tearresistant films according to the invention;

FIG. 8 is an enlarged, vertical sectional view of a second embodiment ofa glazing unit according to the invention and similar to FIG. 7 butfurther including a metalized layer;

FIG. 9 is an enlarged, vertical sectional view of a third embodiment ofa glazing unit according to the invention and similar to FIG. 7 bututilizing a single multilayer tear resistant film according to theinvention; and

FIG. 10 is an enlarged, vertical sectional view of a security controllaminate similar to that illustrated in FIG. 8 but secured to aremovable release liner.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention relates to tear resistant multilayer films comprisinginterdigitated layers of at least one ductile material, at least onestiff material and, optionally, at least one intermediate material. Theexact order of the individual layers is not critical provided that atleast one layer of a stiff material and at least one layer of a ductilematerial are present.

Examples of some film structures within the scope of the inventioninclude:

S(DS)_(x)

D(SD)_(x)

D(ISID)_(y)

S(IDIS)_(y)

wherein S is the stiff material, D is the ductile material, I is theoptional intermediate material, x is a whole number of at least 2(preferably at least 4 and more preferably about 6), and y is a wholenumber of at least 1 (preferably at least 2 and more preferably about3). Other layer arrangements in which the order is essentially randomare also possible. The two outer layers may be the same or may bedifferent. The individual stiff layers may be comprised of the same ordifferent materials so long as the materials are stiff. Similarly, theindividual ductile layers may be comprised of the same or differentmaterials. Preferably, each stiff layer is provided by the same materialand each ductile layer is the same so as to facilitate film production.

A film 10 according to the invention and having the structureD(ISID)_(y), where y is 2 is shown in FIG. 1. Film 10 includes 9alternating layers of ductile material 11, intermediate material 12, andstiff material 13. The two outer layers are formed of ductile material11. However, the structure of FIG. 1 could be such that either stiffmaterial 13 or intermediate material 12 provides the outer layers.Preferably the film comprises at least 5 layers, more preferably frommore than 5 layers (e.g., 9 layers) to 35 layers, and most preferablyabout 13 layers, although as many layers as desired (e.g., 61 layers)may be employed.

The thickness of each layer and the total thickness of the film may bevaried over wide limits within the scope of the invention. The practicalthickness of the film is limited only by the handling characteristicsdesired. The lower useful practical limit is that at which the filmbecomes too flimsy to be readily handled or is no longer sufficientlytear resistant while the upper useful limit is that at which the filmbecomes overly rigid and too difficult to process. Within theseconstraints, films according to the invention typically have a nominalthickness in the range of from about 7 to 500 microns (i.e.,micrometers) (μm) and, more preferably, from about 15 to 185 μm.

The thickness of the individual layers may also vary over a wide range,it being understood that as the number of layers increases at a constantor decreasing film thickness, the thickness of each layer declines. Theindividual layers of stiff material typically have an average nominalthickness of at least about 0.5 μm, more preferably from 0.5 μm to 75μm, and most preferably from about 1 to 25 μm. Although the thickness ofeach layer may be the same, it is preferred that the ductile materiallayers be thinner than the stiff material layers. The ductile materiallayers may range in average nominal thickness from greater than about0.01 μm to less than about 5 μm, more preferably, from about 0.2 to 3μm. All film and layer thickness stated herein are nominal thicknesseswhich may be measured according to the procedure set forth in ASTM TestMethod D 1004.

Stiff materials useful in the practice of the invention comprisepolyesters which are the reaction product of dicarboxylic acid (or esterderivatives thereof) and diol components. Preferably, the dicarboxylicacid component is either terephthalic acid or naphthalene dicarboxylicacid (such as dimethyl 2,6-naphthalene dicarboxylic acid) or esterderivatives thereof, and the diol component is either ethylene glycol or1,4-butanediol. Accordingly, preferred polyesters for use as the stiffmaterial include polyethylene terephthalate, polyethylene naphthalate,polybutylene terephthalate, and polybutylene naphthalate, as well asblends thereof.

Additional stiff copolyesters based on these materials may be made bycopolymerizing the terephthalic and/or naphthalene dicarboxylic acidcomponent(s) with one or more other diacids, including adipic, azelaic,sebacic, isophthalic, dibenzoic and cyclohexane dicarboxylic acids.Similarly, various stiff copolyesters may be formed by copolymerizingthe ethylene glycol and/or 1,4-butanediol component(s) with one or moreother diols such as diethylene glycol, propanediol, polyethyeleneglycol, polytetramethylene glycol, neopentyl glycol, cylcohexanedimethanol, 4-hydroxy diphenol, bisphenol A, and 1,8-dihydroxy biphenyl.Useful stiff materials may also be provided by incorporating one or moreother diacids and/or one or more other diols into the polymerizationmixture. The amount of such other materials may be varied over widelimits so long as the resulting polymer is stiff.

As used herein, "stiff" means stretch resistant, creep resistant anddimensionally stable. More particularly, "stiff" materials according tothe invention are high tensile modulus polyesters and copolyesters,preferably materials having a tensile modulus, at the temperature ofinterest, greater than 200 kpsi (kpsi=1000 pounds per square inch=6.9MPa) (1,380 megaPascals (MPa)), more preferably greater than 300 kpsi(2,070 MPa), and most preferably greater than 400 kpsi (2,760 MPa). Insome instances, orientation may be necessary to achieve the desiredtensile modulus.

Tensile modulus of the stiff material is determined according to ASTMTest Method D 822-88 using a 4 inch (10.2 centimeters (cm)) gauge lengthand a separation rate of 2 inches/minute (5 cm/min). The "temperature ofinterest" means the average temperature at which the film (or astructure incorporating the film) is intended to be used. ASTM D 882-88specifies a test temperature of 23° C.±2° C. If the temperature ofinterest for the multilayer film is within this range, the ASTM testprocedure is followed as published. If, however, the temperature ofinterest is outside this range, then the test procedure is followed withthe exception that the test is performed at the temperature of interest.

Ductile materials useful in the invention generally have a tensilemodulus of less than 200 psi (1,380 MPa) and a tensile elongation, atthe temperature of interest as defined above, of greater than 50%preferably greater than 150%. Tensile modulus and tensile elongation ofthe ductile material are measured in accordance with ASTM Test Method D882-88, a tensile test, using a 4 inch (10.2 cm) gauge length and aseparation rate of 5 inches/minute (12.7 cm/min). "Tensile elongation,"as used herein, refers to the elongation at break of the ductilematerial as measured during the referenced tensile test procedure.

Suitable ductile materials include ethylene copolymers such asethylene/vinyl acetate, ethylene/acrylic acid, ethylene/methyl acrylate,ethylene/methacrylic acid, ethylene/methyl methacrylate, ethylene/ethylacrylate, ethylene/ethyl methacrylate and blends and ionomers thereof.Ethylene/olefin copolymers in which the olefin component is provided bypropylene, butylene or other higher order alpha-olefins may also beused. Preferably, the nonethylene portion of the copolymer comprisesfrom 5% to 30% by weight of the copolymer. Particularly useful areethylene/vinyl acetate copolymers having at least 6 mole % vinylacetate. Examples of suitable commercial materials include the ELVAXseries of ethylene/vinyl acetate copolymers (E.I. dupont de Nemours) andthe ULTRATHENE series of ethylene/vinyl acetates (Quantum ChemicalCorp.).

Suitable ductile materials also include a wide variety of polyesters andcopolyesters which comprise the reaction product of dicarboxylic acid(including ester derivatives thereof) and diol components. Illustrativedicarboxylic acids include terephthalic acid, isophthalic acid,naphthalene dicarboxylic acid, adipic acid, azelaic acid, sebacic acid,and cyclohexane dicarboxylic acid. Diols with which these diacids may bepolymerized include ethylene glycol, diethylene glycol, propanediol,butanediol, neopentyl glycol, polyethylene glycol, polytetramethyleneglycol, poly ε-caprolactone, polyester glycol and cyclohexanedimethanol. The relative amounts of the diacid and diol components maybe varied over wide limits.

A particularly preferred ductile copolyester comprises 60 moleequivalents of terephthalic acid and 40 mole equivalents of sebacic acidto provide the dicarboxylic acid component, and 100 mole equivalents ofethylene glycol for the diol component. Another preferred copolyestercomprises 100 mole equivalents cyclohexane dicarboxylic acid for thedicarboxylic acid component, and 91 mole equivalents cyclohexanedimethanol and 9 mole equivalents polytetramethylene glycol for the diolcomponent. Examples of commercially available copolyester resins whichmay be used to provide the ductile material include ECDEL-9965,ECDEL-9966 and ECDEL-9967 (Eastman Chemical Products, Inc.).

Suitable ductile materials further include polyolefins such aspolyethylene, polypropylene and other higher order polyolefins.

Also useful as ductile materials are polyamides in which thedicarboxylic acid component and the diamine component (of which thepolyamides are the reaction product) each individually have from 2 to 12carbon atoms. The polyamides may be copolymerized with various longchain aliphatic glycols such as polytetramethylene glycol orpolyethylene glycol. The glycol may comprise up to about 25% by weightof the polyamide. Useful polyamides include the PEBAX family of resinscommercially available from Atochem.

Polyurethanes comprising the reaction product of various diioscyanatesor triisocyanates and active hydrogen containing compounds may also besuccessfully employed as ductile materials. Useful diisocyanates andtriisocyanates include hexamethylene diisocyanate, trans-cyclohexane1,4-diisocyanate, isophorone diisocyanate, 2,2,4- and2,4,4-trimethylhexamethylene diisocyanate, m-tetramethylxylenediisocyanate, p-tetramethylxylene diisocyanate, dicyclohexylmethane4,4-diisocyanate, dimethyl diisocyanate, m-phenylene diisocyanate,p-phenylene diisocyanate, toluene 2,4-diisocyanate, toluene 2,6diisocyanate, naphthalene 1,5-diisocyanate, diphenylmethane2,4'-diisocyanate, diphenylmethane 4,4'-diisocyanate, polymethylenepolyphenylene polyisocyanate, triphenylmethane 4,4',4"-triisocyanate,isocyanatoethyl methacrylate, 3-isopropenyl-α,αdimethylbenzyl-isocyanate, and thiophosphoric acid,tris(4-isocyanatophenyl ester), as well blends or mixtures thereof.

Useful active hydrogen containing materials include diols (e.g.,1,4-butanediol, 1,6-hexanediol, castor oil), polyester polyols,polyether polyols, and polyfunctional primary or secondary amines. Theequivalent ratio of diisocyanate to active hydrogen is about 1:1.

It has been found that relatively small amounts of the ductile material(i.e., amounts of less than 5 weight percent), relative to the stiffmaterial, can greatly improve the tear resistance of multilayer filmsmade therewith. However, as little as about 1 weight percent (weight %or wt. %), preferably at least about 2.6 weight %, of the ductilematerial is believed to be sufficient. Ductile material loadings up toabout 10 to 20 weight may be used although exceeding this range mayreduce the tear resistance of films made therewith.

Preferably, films according to the invention have an interlayer adhesionof at least 0.1 pounds/inch width (piw) (18 grams/cm (g/cm)), morepreferably at least 0.5 piw (90 g/cm). Peel adhesion may be tested usingASTM Test Method F904-84 and a separation rate of 2 inches/minute (5cm/min.). What constitutes an acceptable interlayer adhesion will bedictated in large part by the application intended for the multilayerfilm. Thus, if the film provides the backing for an abrasive sandingdisc which may encounter high shear forces in use, an interlayeradhesion of at least 1 piw (180 g/cm), preferably at least 3 piw (540g/cm), may be necessary. On the other hand, for static single useapplications such as shatterproof or anti-lacerative window films, lessinterlayer adhesion such as 0.01 piw (2 g/cm) may be acceptable. More orless interlayer adhesion may be desirable depending on the failure modeof the film as it tears.

Because films of the invention comprise a number of interleaved layersof different materials, it is sometimes necessary to provide a means forincreasing the interfacial adhesion between adjacent layers to achievethe desired interlayer adhesion. Several techniques may be used. Forexample, when the interfacial adhesion between adjacent layers of stiffand ductile components is considered inadequate, a low concentration(e.g. about 0.01 to 10%) of a component which contains an appropriatefunctional group may be incorporated into either or both of the ductileand stiff materials to promote interlayer adhesion. This may beaccomplished by, for example, reacting or blending the functionalgroup-containing component with the ductile or stiff material or bycopolymerizing or blending it with the monomers used to provide theductile or stiff material. Examples of useful adhesion-promoting,functional group-containing components include acrylic acid, methacrylicacid, maleic anhydride, vinyl pyridine, oxazoline-containing materials(such as polyethyl oxazoline), and the like.

Alternatively, a layer of an appropriate intermediate material may beutilized as a tie layer between the layers of stiff and ductilematerials. The intermediate layer may comprise a ductile material, astiff material, or a rubbery material. The intermediate layer could alsocomprise a blend of stiff and ductile materials. Ductile and stiffmaterials are described above. Rubbery materials manifest no significantyield point, but typically display a sigmoidal rise in elongation withapplied load until rupture occurs at high strain. Whatever the precisenature of the intermediate material, if it is being used as a tie layer,it must enhance the adhesion between the stiff and ductile materials.Combinations of these approaches, or even other approaches may also beused.

Many materials are useful as the intermediate layer. They includeethylene/vinyl acetate copolymers, preferably containing at least about10% by weight vinyl acetate and a melt index of about 10, e.g., theELVAX series of materials (duPont); carboxylated ethylene/vinyl acetatecopolymers, e.g., CXA 3101 (duPont); copolymers of ethylene and methylacrylate, e.g., POLY-ETH 2205 EMA (available from Gulf Oil and ChemicalsCo.), and ethylene methacrylic acid ionomers e.g., SURYLN (duPont);ethylene/acrylic acid copolymers; and maleic anhydride modifiedpolyolefins and copolymers of polyolefins, e.g., MODIC resins (availablefrom Mitsubishi Chemical Company).

Other materials useful as the intermediate layer include polyolefinscontaining homogeneously dispersed vinyl polymers such as the VMX resinsavailable from Mitsubishi (e.g., FN70, an ethylene/vinyl acetate-basedproduct having a total vinyl acetate content of 50% and JN-70, anethylene/vinyl acetate-based product containing 23% vinyl acetate and23% dispersed poly(methyl methacrylate)), POLYBOND (believed to be apolyolefin grafted with acrylic acid) available from Reichold ChemicalsInc., and PLEXAR (believed to be a polyolefin grafted with polarfunctional groups) available from Chemplex Company. Also useful arecopolymers of ethylene and methacrylic acid such as the PRIMACOR familyavailable from Dow Chemical Co. and NUCREL available from dupont. Otherethylene copolymers such as ethylene/methyl methacrylate, ethylene/ethylacrylate, ethylene/ethyl methacrylate and ethylene/n-butyl acrylate maybe used.

The various polyesters and copolyesters described above as beingsuitable ductile materials may also function as an intermediate layer.

The intermediate layer preferably comprises from about 1 to 30 (mostpreferably from about 2 to 10) weight % of the film. The nominalthickness of the intermediate layer can vary over a wide range dependingon the number of layers in the multilayer film and the overall thicknessof the film, but preferably is from about 0.01 μm to less than about 5μm, more preferably from about 0.2 to 3 μm.

Alternatively, adjacent layers of stiff and ductile materials may betreated with radiation, such as ultraviolet, electron beam, infrared ormicrowave radiation, to improve adhesion.

Each of the stiff, ductile and intermediate layer materials may furtherinclude or be supplemented with various adjuvants, additives, colorants,extenders, antioxidants, thermal stabilizers, ultraviolet lightstabilizers, plasticizers, slip agents, etc. that are conventionally andcustomarily used in the manufacture of such materials or films madetherewith. These supplemental materials may comprise up to about 5weight % of the total weight of the layers into which they areincorporated so long as the tear resistance of the film is notsignificantly adversely affected.

If desired, a functional layer may be applied to one or both of themajor surfaces of the film. For example, an adhesive 14 may be appliedto at least one of the major surfaces as shown in FIG. 2. Adhesive 14may be activatable by pressure, heat, solvent or any combination thereofand may be of any type such as an acrylate, a rubber/resin, or asilicone. Other functional layers, for example, an abrasive material(optionally in a binder), a radiation (e.g., light) sensitive orblocking layer, an ink-receptive layer, a magnetic recording media, atop coat, a slip agent layer, a vapor coated material, a primer layer, areflective layer, or a moisture or gas barrier layer may be employed.Other functional layers may also be used. The functional layers may beemployed singly or in combination with other functional layers on one orboth sides of the film.

To modify the surface properties of the film or to promote adhesion ofany subsequently applied functional layer, the film may be pretreatedwith a primer coating, activated by flame or corona discharge or othersurface treatments, or a combination of these approaches.

Films according to the invention may be readily made using techniquesknown in the art. One such technique is disclosed in U.S. Pat. No.3,565,985 (Schrenk et al.). In making films of the invention, meltcoextrusion by either the multimanifold die or the feedblock method inwhich individual layers meet under laminar flow conditions to provide anintegral multilayer film may be used. More specifically, separatestreams of the ductile, stiff and, optionally, intermediate materials ina flowable state are each split into a predetermined number of smalleror sub-streams. These smaller streams are then combined in apredetermined pattern of layers of stiff, ductile and, optionally,intermediate materials to form an array of layers of these materials ina flowable state. The layers are in intimate contact with adjacentlayers in the array. This array generally comprises a tall stack oflayers which is then compressed to reduce its height. In themultimanifold die approach, the film width remains constant duringcompression of the stack while the width is expanded in the feedblockapproach. In either case, a comparatively thin, wide film results. Layermultipliers in which the resulting film is split into a plurality ofindividual subfilms which are then stacked one upon another to increasethe number of layers in the ultimate film may also be used.

In manufacturing the films the materials may be fed such that any one ofthe three constitutes the outer layer. The two outer layers oftencomprise the same material. Preferably, the materials comprising thevarious layers are processable at the same temperature and have similarmelt viscosities so as to avoid degrading a lower melting material.Accordingly, residence time and processing temperatures may have to beadjusted depending on the characteristics of the materials of eachlayer.

Other manufacturing techniques such as lamination, coating or extrusioncoating may be used in assembling multilayer films according to theinvention. For example, in lamination, the various layers of the filmare brought together under temperature and/or pressure (e.g., usingheated laminating rollers or a heated press) to adhere adjacent layersto each other. In extrusion coating, a first layer is extruded ontoeither a cast web, a monoaxially oriented film or a biaxially orientedfilm and subsequent layers are sequentially coated onto the previouslyprovided layers. Exemplary of this method is U.S. Pat. No. 3,741,253.Extrusion coating may be preferred over the melt coextrusion processdescribed above where it is desirable to pretreat selected layers of themultilayer film or where the materials are not readily coextrudable.

It is preferred that the layers of the stiff material be oriented,either uniaxially or biaxially, at a temperature above their glasstransition temperature so as to enhance the stiffness, modulus and creepresistance of the film. (For some uses, such as thermoformingapplications, orientation of the stiff material layers would not berequired.) Orientation of the ductile and intermediate layer materialsis optional. Orientation may be accomplished by conventional methodstypically used in the art such as mechanical stretching (drawing) ortubular expansion with heated air or gas. Typical draw ratios are in therange of 2.5 to 6 times in either or both of the machine and transversedirections. Greater draw ratios (for example, up to about 8 times) maybe used if the film is oriented in only one direction. The film need notbe stretched equally in the machine and transverse directions althoughthis is preferred if balanced properties are desired.

The films may also be heat set by exposing the film to a temperature ofabout 10° to 150° C. below the melting temperature of the stiffcomponent for about 4 to 15 seconds so as to increase the crystallinity,stiffness, modulus and creep resistance of the film while reducing itstendency to shrink. In applications where film shrinkage is not ofsignificant concern, the film may be heat set at relatively lowtemperatures or not at all. On the other hand, as the temperature atwhich the film is heat set is increased, the tear resistance of the filmmay change. Thus, the actual heat set temperature and time will varydepending on the composition of the film and perhaps its intendedapplication but should not be selected so as to substantially degradethe tear resistant properties of the film. Within these constraints, aheat set temperature of about 135° to 205° C. is generally desirable formany of the applications in which the multilayer films of the inventionare useful.

Various functional layers may be subsequently applied by lamination,extrusion coating or other known techniques. Various primers and/orsurface treatments may be required as discussed more fully above.

Multilayer films according to the invention are both stiff(dimensionally stable, high modulus) and tear resistant. As explainedabove, stiff, high tensile modulus, creep resistant films such ascellophane, polyester and biaxially oriented polypropylene packagingfilms have little tear resistance. On the other hand, low tensilemodulus, ductile materials such as polyolefin trash bags are tearresistant but are not dimensionally stable (i.e., they stretch readily).Films according to the invention provide the desirable properties ofboth high tensile modulus, stiff, dimensionally stable, creep resistantmaterials and low tensile modulus, ductile, tear resistant materials ina multilayer arrangement. As a result, multilayer films according to theinvention offer both excellent tear resistance and dimensionalstability. This beneficial amalgamation of properties is achievedbecause the different materials which comprise the films of theinvention are assembled in a multilayer arrangement. As exemplifiedbelow, single layer blends of stiff and ductile polymers do not equallyreflect the characteristics of films according to the invention.

The tear resistance of films according to the invention may be measuredby ASTM Test Method D 1004 (also known as a Graves tear test). In aGraves tear test, a film sample 16 having the general shape shown inFIG. 3 (and described more explicitly in ASTM D 1004) is clamped betweenopposed jaws with an initial separation of 1 inch (2.5 cm). The jaws arethen moved apart at a constant rate of 2 inches/minute (5 cm/min.) totear the film in the area of the sample designated by the referencenumeral 18. The tearing stresses imposed on the film are concentrated inarea 18. The film may be torn in either the machine direction (i.e., thedirection in which the film is extruded) or the transverse direction(i.e., perpendicular to the machine or extrusion direction). The teardirection corresponds to the orientation of area 18. More specifically,a pair of axes labeled A-B and C-D have been superimposed on film sample16 in FIG. 3. The opposed jaws are moved along axis A-B to tear filmsample 16 along axis C-D.

With reference to FIG. 4, test data were recorded by graphicallyplotting the stress (as measured in kpsi) experienced by the film versusthe strain (as measured by Graves elongation in %) that the filmunderwent during the test. "Stress" is defined as the recorded forcedivided by the product of the film thickness and the ligament width(distance "d" in FIG. 3). The expression "Graves elongation" as usedherein refers to the elongation of a film in the tear direction asobserved during a Graves area test and reflects the percent change inthe jaw separation distance that occurs during the test relative to thejaw separation distance at the outset of the test. "Graves elongation atbreak" as used herein refers to the elongation of the film in % at itsbreak point observed during the Graves area test. (It will be understoodthat Graves elongation at break differs from tensile elongation. Tensileelongation is measured during a tensile test and may be used tocharacterize ductile materials useful in the invention as explainedabove.)

With continued reference to FIG. 4, the plot (i.e., "curve") labeledwith the letter "A" describes a film having a large maximum stress whichfalls off quickly as the film is stretched during the test. Curve Atypifies the performance of a high modulus, stiff, dimensionally stablematerial which has poor tear resistance (as shown by the rapid falloffin stress as the film tears). Polyesters, cellophane, biaxially orientedpolypropylene and similar packaging films perform similarly to curve A.Curve A was obtained by measuring the performance of the polyethyleneterephthalate film of comparative example 15, described more fullybelow.

The curve labeled with the letter "B" describes the performance of a lowmodulus, ductile, readily stretchable, traditionally tear resistantmaterial (as evidenced by the relatively high Graves elongation at breakrelative to curve A) because the film stretches rather than tears. Thefilm is capable of sustaining only a relatively low stress. Plastictrash and grocery bags are common examples of films that would performin a manner similar to that described by curve B. Curve B was obtainedby measuring the performance of the linear low density polyethylene filmof comparative example 16, described more fully below.

Curve "C" illustrates the performance of a multilayer film according tothe invention and, more specifically, the film of example 39 describedbelow. The maximum stress sustained by this film is similar to orexceeds the stiff film of curve A. However, the stress experienced bythe curve C film of the invention does not fall off as rapidly as in thecase of the curve A film. Thus, as compared to conventional polyesterfilms of curve A, films according to the invention are more able tosuccessfully withstand catastrophic tearing forces while being ofsubstantially equal modulus. Such a property is highly desirable incertain applications, especially shatterproofing film for windows wherethe impact from breaking glass may be sudden and catastrophic. Ascompared to the low modulus films of curve B, films of the invention areable to sustain much higher stress. Thus, films according to theinvention are both stiff (high modulus) and tear resistant.

In a Graves tear test, tear resistance data are conventionally reportedas the maximum force experienced by the film. The data reported herein,however, are the total area (referred to herein at times as the "Gravesarea") beneath the stress-strain curve (i.e., the curves of FIG. 4)which is obtained by a mathematical integration of the curve. Gravesarea is regarded as a measure of the total energy required to cause thefilm to fail and, hence, a measure of the film's combined stiffness andtear resistance. Thus, Graves area may be regarded as a measure of theability of the film to absorb energy. Graves area is reported herein inunits of kpsi % wherein 1 kpsi %=69 kilojoules/cubic meter. It will beunderstood that films with a relatively large Graves area have enhancedcombined stiffness and tear resistance relative to those films with arelatively small Graves area.

As shown more fully below, Graves area may vary depending on whether thetest is conducted in the machine or the transverse direction of thefilm. Also, Graves area generally increases with increasing filmthickness. As a general characterization, a multilayer film may beregarded as tear resistant within the scope of the invention if itdemonstrates a Graves area in one direction which exceeds the Gravesarea (in the same direction) of a single layer film that comprises onlythe stiff polyester or copolyester used in the multilayer film, thesingle layer film being processed (i.e., oriented, heat set etc.) in thesame manner as the multilayer film and to a substantially equal filmthickness. Preferably and more specifically, a multilayer film may beregarded as tear resistant within the scope of the invention if itdemonstrates a Graves area at least equal to 40+0.4(x) kpsi % in onedirection (e.g., the machine or the transverse direction) of the film,wherein x is the nominal thickness of the film in microns.

Furthermore, and related to their overall performance, multilayer filmsof the invention preferably have a tensile modulus (when testedaccording to ASTM Test Method D 882-88) of at least 175 kpsi (1,208 MPa)in one direction of the film, more preferably at least 240 kpsi (1,656MPa), and most preferably at least 450 kpsi (3,105 MPa). However, theactual modulus which is desirable will depend on the application forwhich the film is intended, some applications preferring relativelystiffer films and others preferring relatively more flexible films. Inaddition, and also related to their overall performance, multilayerfilms according to the invention desirably demonstrate a Graveselongation at break of at least 20%, more preferably at least 40% in thetear direction of the film measured during the Graves area test.

The invention will be more fully appreciated with reference to thefollowing, nonlimiting examples.

EXAMPLES 1 to 26

A series of multilayer films comprising alternating layers of a stiffmaterial and a ductile material was formed by coextruding polyethyleneterephthalate (PET) (differential scanning calorimetry (DSC) meltingpoint of 256° C.; intrinsic viscosity of 0.60 deciliters per gram (dl/g)as measured in 60% phenol and 40% dichlorobenzene at 110° C.) as thestiff material with a copolyester as the ductile material. Thecopolyester comprised 40 mole % (or mole equivalents herein as thereactive systems are based on 100 equivalents) sebacic acid and 60 mole% terephthalic acid as the dicarboxylic acid components, and 100 mole %ethylene glycol as the diol component. The copolyester had an intrinsicviscosity in the range of 0.9 to 1.05 dl/g when measured in the samefashion as the PET. The ductile copolyester also displayed a tensilemodulus of 14 kpsi (97 kPa) and a tensile elongation of 355% when testedaccording to ASTM D822-88 at room temperature but using a separationrate of 5 inches/minute (12.7 cm/minute).

The multilayer films were coextruded onto a chilled casting wheel andsubsequently oriented sequentially 2.6 times in the machine direction(MD) at 80° C. and 4.2 times in the transverse direction (TD) at 99° C.The films were then heat set at 149° C.

The number of layers, the film thickness, and the weight percent of theductile copolyester were varied as shown below in Table 1. The tearresistance of the films in both the machine and the transversedirections are reported below in Table 1 as Graves area (rounded to thenearest 10 here and for other examples) according to the proceduredescribed more fully hereinabove. The Graves elongation at break values(rounded to the nearest 5 here and for other examples) are also reportedin Table 1. The reported Graves area and Graves elongation at breakvalues throughout the application (unless noted otherwise) are anaverage of 9 readings in each of the machine and transverse directions.

Although ASTM D 1004 utilizes a 0.5 inch (1.3 cm) ligament (distance "d"in FIG. 3), examples 1 to 26 herein were analyzed using a 1.31 inch (3.3cm) ligament. For examples 1 to 26, the observed Graves area resultswere mathematically converted to a value corresponding to a 0.5 inch(1.3 cm) ligament by multiplying the observed result by 0.678 and adding32.4, this conversion factor having been determined by a linearregression analysis of multiple samples. The observed results for Graveselongation at break for examples 1 to 26 were also mathematicallyconverted so as to correspond to a 0.5 inch (1.3 cm) ligament bymultiplying the observed result by 0.655 and adding 11.3, thisconversion factor having been determined by a linear regression analysisof multiple samples.

                  TABLE 1                                                         ______________________________________                                                                              Graves                                                 Film           Graves  Elongation                                    Number   Thick-  Wt. % of                                                                             Area    at                                      Ex-   of       ness    Ductile                                                                              (kpsi %)                                                                              Break (%)                               ample Layers   (μm) Material                                                                             MD   TD   MD    TD                              ______________________________________                                         1     5       54.6    10     160  160  40    40                               2     5       54.1    20     110  130  30    35                               3     5       47.8    30     120  130  35    40                               4     5       45.7    40      80  110  25    40                               5     5       45.7    50      60   80  20    35                               6    13       45.7    10     190  190  30    40                               7    13       57.7    10     240  210  45    45                               8    13       54.6    20     160  150  35    40                               9    13       49.5    30      80  100  25    35                              10    13       53.3    40      90   90  30    35                              11    13       48.3    50      70   80  25    30                              12    29       45.7    10     190  130  35    30                              13    29       46.5    20     110   80  30    30                              14    61       47.5    10     130  100  30    30                              15    61       53.3    20     120   80  30    25                              16    61       53.3    30     100   80  25    30                              17    61       53.3    40      80   70  25    25                              18    61       50.8    50      70   60  25    25                              19     5       27.9    10     130  120  25    30                              20    13       25.4    10     140  130  30    30                              21    29       26.2    10      90   70  20    20                              22    61       24.1    10     110   80  25    20                              23     5       15.2    10      90   90  20    25                              24    13       14.0    10      80   70  20    20                              25    29       15.2    10      80   70  20    20                              26    61       12.7    10      60   50  15    15                              ______________________________________                                    

The data of Table 1 show that as the number of layers in the filmremains constant, the Graves area of the film decreases as the amount ofductile material increases above 10%. The data of Table 1 further showthat as the total number of layers increases, the tear resistance of thefilms tends to increase and then becomes more constant or decreases asthe number of layers approaches 61, especially at lower wt. % amounts ofthe ductile material. Consequently, films according to the inventioncomprise at least 5 layers, more preferably from more than 5 layers to35 layers, and most preferably about 13 layers.

FIG. 5 is a graphical representation of the data of examples 1 to 18,the plotted Graves area being an average of the MD and TD values fromTable 1. FIG. 5 illustrates the relationship among Graves area, the wt.% of the ductile material, and the number of layers in the film as thetotal film thickness was attempted to be held relatively constant. Usinglinear regression analysis, the lines which "best fit" the data sets(based on the number of layers in the film) were drawn.

However, as shown in examples 19 to 26, tear resistance is also relatedto film thickness and the above trends may not always be rigidlyobserved as film thickness decreases. Thicker multilayer films generallyhave enhanced tear resistance relative to thinner multilayer films whenthe number of layers and the amount of ductile material are essentiallyconstant.

COMPARATIVE EXAMPLES 1 to 6

Comparative examples (C.E.) 1 to 6 report a series of single layer filmsformed by extruding the PET of examples 1 to 26 onto a chilled wheel.The films were sequentially drawn 3.5 to 4 times in the machinedirection at about 85° to 90° C., and then about 4.5 times in thetransverse direction at about 100° C. The films were subsequently heatset at 220° to 225° C. The films so produced were regarded asrepresentative of conventional, commercially available PET films such asmight be used in packaging applications. The films were tested forGraves area and Graves elongation at break in both the machine andtransverse directions according to the procedures described above andwith the results shown below in Table 2.

(The processing conditions in the preparation of these comparativeexamples were not identical to those used in preparing examples 1 to 26.It will be understood by those of ordinary skill in the art thatadjustments in processing conditions can affect film properties.However, the films of comparative examples 1 to 6 are regarded asrepresentative of conventional, commercially available PET films. Othercomparative data which replicate examples herein may be found inconjunction with examples 38 and 39, for instance.)

                  TABLE 2                                                         ______________________________________                                                                    Graves                                                            Graves      Elongation                                               Film     Area        at Break                                                 Thickness                                                                              (kpsi %)    (%)                                               Example  (μm)    MD      TD    MD     TD                                   ______________________________________                                        C.E. 1   11.9       40      30     5     10                                   C.E. 2   22.4       60      40    10     10                                   C.E. 3   35.0       40      50    10     15                                   C.E. 4   45.5       40      50    15     10                                   C.E. 5   96.3       70      70    15     20                                   C.E. 6   174.0      90      80    20     20                                   ______________________________________                                    

The data of examples 1, 6, 7, 12, 14, and to 26 were graphically plottedin FIG. 6 to illustrate the relationship among Graves area, filmthickness, and the number of layers as the wt. % of the ductile materialwas held constant at 10%. Separate curves were then constructed for the5, 13, 29 and 61 layer films in both the machine and transversedirections by serially connecting the data points. Separate curves werealso prepared in the machine and transverse directions for the singlelayer PET films of comparative examples 1 to 5. (Comparative example 6was not included in FIG. 6 in order to facilitate data management andpresentation of the graph.) As shown in FIG. 6, multilayer filmsaccording to the invention, virtually without exception, demonstrated aGraves area which exceeded that observed for the conventional PET filmsof comparative examples 1 to 5, whether tested in the machine or thetransverse direction.

Also shown in FIG. 6 is the line defined by the equation 40+0.4(x) kpsi% wherein x is the nominal thickness of the film in microns. Multilayerfilms according to the invention have Graves area values which fallabove this line whereas the conventional PET films of comparativeexamples 1 to 5 have Graves area values which fall below this line. Thuspreferred multilayer films comprising alternating layers of a stiffpolymeric material, a ductile polymeric material, and, optionally, anintermediate material, according to the invention are considered to betear resistant if they demonstrate a Graves area which is equal to orwhich exceeds 40+0.4(x) kpsi % wherein x is the nominal thickness of thefilm in microns. As explained above and related to their overallperformance, tear resistant films of the invention also preferablyexhibit a tensile modulus in one direction of the film of at least 175kpsi (1,203 MPa), more preferably at least 240 kpsi (1,650 MPa), andmost preferably at least 450 kpsi (3,105 MPa) as well as a Graveselongation at break of at least 20%, preferably at least 40%.

EXAMPLES 27 to 31

A series of films comprising a total of 13 alternating layers of thestiff material of examples 1 to 26 and a ductile material provided byECDEL 9966 (believed to be a copolyester based on 1,4-cyclohexanedicarboxylic acid, 1,4-cyclohexane dimethanol, and polytetramethyleneether glycol) was coextruded onto a chilled quenching wheel. When testedaccording to the procedures described in examples 1 to 26 for theductile copolyester, the ductile material of examples 27 to 31 was foundto have a tensile modulus of 26 psi (179 MPa) and a tensile elongationof 630%. The films were subsequently simultaneously oriented 3.3 timesin both the machine and transverse directions at 99° C. and heat set at135° C. The film thickness and the relative amounts of the ductilematerial were varied as shown below in Table 3. The Graves area, tensilemodulus, and Graves elongation at break were tested in the machine andtransverse directions as described above with the results shown below inTable 3.

                                      TABLE 3                                     __________________________________________________________________________    Film       Wt. %                                                                              Graves  Tensiie Graves Elongation                             Thickness  Ductile                                                                            Area (kpsi %)                                                                         Modulus (kpsi)                                                                        at Break (%)                                  Example                                                                            (μm)                                                                             Material                                                                           MD  TD  MD  TD  MD   TD                                       __________________________________________________________________________    27   46.0  2.6  340 230 560 610 35   30                                       28   47.5  4.1  440 180 555 595 80   50                                       29   49.8  6.9  320 240 550 570 65   65                                       30   50.8  9.7  330 280 525 545 70   65                                       31   52.8  12.2 270 300 590 545 65   70                                       __________________________________________________________________________

The data of Table 3 show the benefit of the multilayer films of theinvention including at least about 2.6 weight % of the ductile material.Acceptable Graves area and tensile modulus values were observed as theweight % varied from 2.6 to 12.2. Even when the amount of the ductilematerial was less than 5 wt % useful Graves area and tensile modulusvalues were obtained.

EXAMPLES 32 to 34

A series of films comprising 13 alternating layers of a stiff PET (DSCmelting point=256° C.; intrinsic viscosity=0.72 dl/g) coextruded with aductile ethylene/vinyl acetate copolymer having 18% vinyl acetate and amelt index of 8.0 (measured by ASTM Test Method D 1238 in all examples)was cast onto a chilled quenching wheel. The films were subsequentlysequentially oriented 3.2 times at 93° C. in the machine direction and3.5 times at 102° C. in the transverse direction followed by heatsetting at 204° C. The thickness of each film was approximately 48 μm.The weight % of the ductile material was varied as shown below in Table4 along with the Graves area and Graves elongation at break test data.The reported data are an average of 5 readings in each of the machineand transverse directions.

                  TABLE 4                                                         ______________________________________                                                                     Graves                                                            Graves      Elongation                                                        Area        at Break                                         Wt. %            (kpsi %)    (%)                                              Example Ductile Material                                                                           MD      TD    MD    TD                                   ______________________________________                                        32       5           190     170   40    40                                   33      10           220     230   45    45                                   34      20           180     180   50    45                                   ______________________________________                                    

Table 4 shows the utility of using about 5 to 20 weight % of the ductilematerial although ductile material amounts of 10 weight % or lessprovide the desired effect.

EXAMPLE 35

A film comprising a total of 13 alternating layers of the stiff materialof examples 32 to 34 and 20 weight % of a ductile ethylene/vinyl acetatecopolymer having 25% vinyl acetate and a melt index of 19 was coextrudedand processed as described in conjunction with examples 32 to 34 withthe exception that the film thickness was 42 μm. The film of thisexample had a Graves area of 160 kpsi % in the machine direction and 190kpsi % in the transverse direction, and a Graves elongation at break of35% in the machine direction and 40% in the transverse direction, thereported data being an average of 5 measurements in each direction.

EXAMPLE 36

A 13 layer film according to example 35 was produced with the exceptionthat the ductile material was an ethylene/vinyl acetate copolymer having9% vinyl acetate and a melt index of 7 and the film thickness was 50 μm.The film of this example demonstrated a Graves area of 190 kpsi % in themachine direction and 200 kpsi % in the transverse direction, and aGraves elongation at break of 50% in each of the machine and transversedirections, the reported data being an average of 5 measurements in eachdirection.

EXAMPLE 37

An approximately 50 μm thick 13 layer film was produced according to theprocedure of examples 32 to 36 except using the stiff PET of examples 1to 26 and 10 weight % of a ductile ethylene/vinyl acetate copolymerhaving 18% vinyl acetate and a melt index of 8. The film of this examplehad a Graves area of 220 kpsi % in the machine direction and 240 kpsi %in the transverse direction, and a Graves elongation of 45% in each ofthe machine and transverse directions, the reported data being anaverage of 5 measurements in each direction.

EXAMPLE 38

A 13 μm thick multilayer film was produced comprising a total of 13alternating layers of a stiff PET (DSC melting point=256° C., intrinsicviscosity=1.04) coextruded with a ductile segmented block copolymercomprising nylon 12 and polytetramethylene glycol (68% by weight nylonblock). The film comprised 90 wt. % of the stiff material and 10 wt. %of the ductile material. The film was extruded onto a chilled castingwheel, simultaneously biaxially oriented at 110° C. 4.5 times in each ofthe machine and transverse directions, and heat set at 150° C. The filmexhibited a Graves area of 70 kpsi % in each of the machine andtransverse directions as well as a tensile modulus of 635 kpsi in eachof the machine and transverse directions, which represent an average of5 measurements in each direction. A similar film produced in the samemanner but having 90% by weight of the nylon block in the ductilecopolymer exhibited a Graves area of 10 kpsi % (13 kpsi % observed) ineach of the machine and transverse directions as well as a tensilemodulus of 685 kpsi in each direction (average of 5 measurements).

When a single layer film comprising only the stiff PET was extruded,biaxially drawn and heat set in the same manner and at a thickness of 13μm, it demonstrated an average Graves area of 6 kpsi %, a tensilemodulus of 795 kpsi, and a Graves elongation at break of 2.5% in themachine and transverse directions. Compared to the relatively thickerfilms of some of the preceding examples, the films of example 38 had areduced Graves area. However, as compared to the single layer PET film,even the relatively thin films of this example demonstrated an improvedGraves area. In particular, the second multilayer film, while notsatisfying the Graves area equation which describes the preferred filmsof the invention, had a Graves area of about double that of the singlelayer PET film.

EXAMPLE 39

A film comprising a total of 13 alternating layers of the stiff PET ofexamples 1 to 26 coextruded with 5 weight % of the ductile material ofthe same examples was prepared. The film was cast onto a chilledquenching wheel, sequentially oriented 2.6 times in the machinedirection at 86° C. and 4.5 times in the transverse direction at 103°C., and heat set at 149° C. The film was about 62 μm thick and displayeda Graves area of 330 kpsi % in the machine direction and 220 kpsi % inthe transverse direction. The film also exhibited a tensile modulus of500 kpsi in the machine direction and 700 kpsi in the transversedirection, and a Graves elongation at break of 45% in each direction.The multilayer film of this example was used to prepare curve C of FIG.4.

When a single layer film comprising only the stiff PET of this examplewas extruded, biaxially drawn and heat set in the same manner at athickness of about 66 μm, it demonstrated a Graves area of 120 kpsi % inthe machine direction and 80 kpsi % in the transverse direction. Thesingle layer film also displayed a tensile modulus of 530 kpsi in themachine direction and 730 kpsi in the transverse direction. (Datareported for the single layer PET film are an average of 5 measurementsin each direction.) Even though the tensile moduli of the multilayer andsingle layer films were comparable, the multilayer film demonstratedsuperior tear resistance as measured by the Graves area test.

EXAMPLE 40

A film having a total of 13 alternating layers of a stiff copolyestercomprising 85 mole % terephthalic acid and 15 mole % sebacic acid as thedicarboxylic acid components and 100 mole % ethylene glycol as the diolcomponent, and 10 weight % of a ductile polyurethane (ESTANE 58277), wascoextruded onto a chilled quenching wheel, simultaneously oriented 3.5times in each of the machine and transverse directions at 100° C., andheat set at 149° C. The film had a thickness of about 69 μm anddisplayed a Graves area of 160 kpsi % in the machine direction and 190kpsi % in the transverse direction. The film further exhibited a tensilemodulus of 180 kpsi in the machine direction and 190 kpsi in thetransverse direction. The film also demonstrated a Graves elongation atbreak of 45% in each of the machine and transverse directions. The dataare an average of 5 measurements in each of the machine and transversedirections.

EXAMPLE 41

A multilayer film comprising three different materials coextruded in theconfiguration S(IDIS)y and having a total of 45 layers (y=11) wasprepared. The "S" (stiff) material was the stiff PET of examples 1 to26, the "I" (intermediate) material was an ethylene/vinyl acetatecopolymer tie layer having 18% vinyl acetate and a melt index of 8, andthe "D" (ductile) material was a ductile, low density (0.916 grams percubic centimeter) polyethylene having a melt index of 3.5. The stiffmaterial provided 90 weight % of the film, the intermediate materialprovided 4 weight %, and the ductile material provided 6 weight %. Thefilm was extruded onto a chilled casting wheel and biaxially oriented3.2 times in each of the machine and transverse directions at 100° C.and heat set at 204° C. The 61 μm thick film exhibited a Graves area of70 kpsi % in the machine direction and 100 kpsi % in the transversedirection as well as a Graves elongation at break of 25% in the machinedirection and 30% in the transverse direction.

COMPARATIVE EXAMPLES 7 to 10

A series of three layer films was prepared by coextruding the ductilematerial of examples 27 to 31 with two layers of the stiff PET ofexamples 1 to 26, the PET providing the two outer layers. The films wereextruded onto a chilled casting wheel, simultaneously biaxially drawn at99° C., and heat set at 149° C. The films of comparative examples 7 and8 were biaxially drawn 3.3 times in each of the machine and transversedirections. The films of comparative examples 9 and 10 were biaxiallydrawn 4.0 times in each of the machine and transverse directions. Filmthickness and the wt. % of the ductile material were varied as shownbelow in Table 5. Table 5 also reports the Graves area for each film.Also repeated is example 30 which utilizes the same stiff and ductilepolymers as comparative examples 7 to 10 except in a 13 layerarrangement. The film processing conditions were the same as forcomparative examples 7 and 8 except that the film was heat set at 135°C., a difference which is not believed to have significantly affectedthe results.

                  TABLE 5                                                         ______________________________________                                               Film     Wt. % of   Graves                                                    Thickness                                                                              Ductile    Area (kpsi %)                                      Example  (μm)    Material   MD     TD                                      ______________________________________                                        C.E. 7   45.7       10         200    180                                     C.E. 8   29.5       35         130    150                                     C.E. 9   35.6       10         220    180                                      C.E. 10 34.3       35         110    120                                     30       50.8       9.7        330    280                                     ______________________________________                                    

Table 5 shows that example 30 as compared to comparative example 7 hadan increased Graves area. Although, the 3 layer films of comparativeexamples 7 to 10 did not tear immediately (i.e., they elongated by about10%), some samples failed catastrophically (i.e., they had a Graveselongation at break of less than 10%). The film of example 30, on theother hand, experienced fewer catastrophic failures. Hence, the film ofexample 30 was regarded as better than the films of comparative examples7 to 10.

COMPARATIVE EXAMPLES 11 to 14

A series of comparative examples was prepared by extruding the stiff andductile materials of examples 1 to 26 into a blended single layer filmrather than a multilayer film. The single layer films were extruded ontoa chilled casting wheel, biaxially oriented 3.3 times in each of themachine and transverse directions at 100° C., and heat set at 140° C.The weight % of the ductile material was varied as shown below in Table6 along with the results of the Graves area and Graves elongation atbreak tests, the reported data being an average of 5 measurements ineach direction. The films were not sufficiently uniformly thick topermit Graves area, tensile modulus and Graves elongation at breaktesting at one thickness in both the machine and transverse directions.Consequently, Table 6 also reports the film thickness for testing ineach direction, the reported thickness being an average of 5measurements in each direction.

                                      TABLE 6                                     __________________________________________________________________________               Film   Tensile       Graves                                        Wt. % of   Thickness                                                                            Modulus                                                                              Graves Area                                                                          Elongation                                    Ductile    (μm)                                                                              (kpsi) (kpsi %)                                                                             at Break (%)                                  Example                                                                             Material                                                                           MD TD  MD TD  MD  TD MD  TD                                        __________________________________________________________________________    C.E. 11                                                                              0   33 39  640                                                                              640 70  100                                                                              20  30                                        C.E. 12                                                                              5   43 25  420                                                                              450 80  110                                                                              30  35                                        C.E. 13                                                                             10   27 38  440                                                                              570 80   80                                                                              30  25                                        C.E. 14                                                                             30   80 59  410                                                                              420 80  110                                                                              30  35                                        __________________________________________________________________________

Comparative examples 11 to 14 illustrate that blends of stiff andductile materials extruded as single layer films do not exhibit anysignificant improvement in tear resistance with the addition of aductile material. This is in distinction to the benefits which areachieved by coextruding the stiff and ductile materials into amultilayer film according to the invention.

COMPARATIVE EXAMPLE 15

Comparative example 15 describes the preparation of the single layer PETfilm measured by curve A of FIG. 4. More specifically, the PET ofexamples 1 to 26 was melt extruded onto a chilled casting wheel and thensequentially oriented 3.4 times in the machine direction at 88° C. and4.0 times in the transverse direction at 110° C., followed by heatsetting at 232° C. The finished film was 51 μm thick and demonstrated aGraves area of 30 kpsi % in the machine direction and 40 kpsi % in thetransverse direction as well as a tensile modulus of 660 kpsi in themachine direction and 650 kpsi in the transverse direction. The filmexhibited a Graves elongation at break of 10% in each direction. Thefilm of this example is considered representative of a conventionalbiaxially oriented PET film.

COMPARATIVE EXAMPLE 16

Comparative example 16 describes the preparation of the single layerlinear low density polyethylene film measured by curve B of FIG. 4. Morespecifically, TF0119F linear low density polyethylene (hexene comonomer)having a density of 0.918 grams/cubic centimeter and commerciallyavailable from Novacor Chemicals, Inc. (Calgary, Alberta) was extrudedand blown into a 51 μm thick film. The blow up ratio was 3.2 and thedraw down ratio was 12.3. The film demonstrated a Graves area of 180kpsi % in the machine direction and 200 kpsi % in the transversedirection due significantly to the large Graves elongation at break(greater than 180%). However, the film exhibited a relatively lowstress. The film of this example is considered representative of filmsconventionally employed in the manufacture of garbage and grocery bags.

EXAMPLES 42 to 45 COMPARATIVE EXAMPLES 17 and 18

A series of examples was prepared to illustrate the improvement in tearresistance that is possible when multilayer films comprising alternatinglayers of stiff and ductile materials are oriented in only onedirection. More specifically, a series of 13 layer films having thecomposition of the film of example 39 (the PET of examples 1 to 26 with5 wt. % of the ductile material of the same examples) was extruded ontoa chilled casting wheel. A square sample of each film was clamped on allfour sides and drawn at 100° C. 4.0 times in one direction at a constantwidth while being restrained in the transverse direction. The film wasthen heat set at 150° C. The tear resistance of the film and the Graveselongation in the direction of orientation (MD) and the directionperpendicular thereto (TD) were tested as described above with theresults shown below in Table 7. Also evaluated and reported in Table 7as comparative examples 17 and 18 are two single layer films comprisingthe PET of example 39 processed as described for examples 42 to 45.

                  TABLE 7                                                         ______________________________________                                                                    Graves                                                            Graves      Elongation                                               Film     Area        at Break                                                 Thickness                                                                              (kpsi %)    (%)                                               Example  (μm)    MD      TD    MD     TD                                   ______________________________________                                        42        89        80      NT    30     NT                                   43       117        40      540   50     105                                  44       131        20      540   10     110                                  45       252        60      440   25     110                                  C.E. 17   90        10      NT     5     NT                                   C.E. 18  120        10      400   10      90                                  ______________________________________                                         NT Not tested                                                            

These examples show that uniaxially oriented multilayer films accordingto the invention can offer improved tear resistance relative to singlelayer films comprising only a stiff PET.

EXAMPLES 46 to 49

Four 13 layer uniaxially oriented films were prepared according to theprocedure described in conjunction with examples 42 to 45 except thatthe films were drawn either 3.5 times or 4.0 times (as reported below inTable 8) and the film composition was different. The films comprised thestiff PET of examples 27 to 31 coextruded with 5 wt. % of the ductilematerial of the same examples (ECDEL 9966). The tear resistance andGraves elongation at break of the films were tested as described abovewith the results shown below in Table 8.

                  TABLE 8                                                         ______________________________________                                                                          Graves                                                             Graves     Elongation                                  Film                   Area       at Break                                    Thickness     Draw     (kpsi %)   (%)                                         Example (μm)   Ratio    MD    TD   MD    TD                                ______________________________________                                        46      160       3.5      100   NT   40    NT                                47      180       3.5      NT    420  NT    100                               48      138       4.0       70   NT   30    NT                                49      150       4.0      N     450  NT    100                               ______________________________________                                         NT = Not tested                                                          

Examples 46 to 49 were not tested for Graves area and Graves elongationat break in both the machine and transverse directions as insufficientmaterial existed for preparing appropriate samples for testing in bothdirections. While examples 46 and 48 do not satisfy the equation fortear resistance provided above for preferred films when tested in themachine direction, it is believed that such samples would meet thisequation when tested in the transverse direction as evidenced by thetransverse direction Graves area data obtained for examples 47 and 49.Furthermore, and although there is a difference in thickness amongexamples 46 and 48 and comparative examples 17 and 18 (see Table 7), thesignificant improvement in the machine direction tear resistance ofexamples 46 and 48 versus the comparative examples is believed to berepresentative of the benefits which can be realized by uniaxiallyorienting a multilayer film according to the invention as compared to asingle layer PET film.

As noted above, the combination of tear resistance and high modulusprovides the multilayer films of the present invention with a uniqueability to absorb energy, especially in the event of a catastrophicimpact. Consequently, the multilayer films disclosed herein are usefulas security control laminates for shatter-proofing glazing membersagainst impact or explosion. In such applications, one or more tearresistant multilayer films are applied to a glazing member as a shieldthat prevents the fragmentation of the glazing member even though itsplinters or shatters upon breaking. When adhesively bonded to a glazingmember, security control laminates based on the multilayer films of thepresent invention provide excellent energy absorption and distributionproperties without significantly delaminating from the glazing member.The security control laminates are also less likely to puncture and/ortear.

Turning now to FIG. 7, a glazing unit 20 comprises a security controllaminate 21 bonded to the interior face of a glazing member 22 by meansof an adhesive layer 23, such as those commonly used for solar controlor security films, including acrylate pressure-sensitive adhesives andwater activated adhesives. Security control laminate 21 comprises afirst multilayer film 25 (having a first face 25a and an opposed secondface 25b) and a second multilayer film 27 (having a first face 27a andan opposite second face 27b) the two films being secured or bondedtogether by a layer of a (polyester) laminating adhesive 26.

In order to minimize the deteriorative effects of ultraviolet (UV)radiation on any of the polymeric materials which comprise the securitycontrol laminate, it is highly desirable to interpose a coating 24,containing a UV absorber, between multilayer film face 25b and adhesivelayer 23. Alternatively, means for absorbing UV radiation may beincorporated into adhesive layer 23 or multilayer film 25. Suitable UVabsorbent coatings may include substituted benzophenones and substitutedbenzotriazenes.

Multilayer film face 27b optionally includes a thin, abrasion resistantcoating 28 thereon to protect film 27 from mechanical abrasion such asmight occur during installation or cleaning of the security controllaminate. Suitable abrasion resistant coatings comprise photopolymerizedmaterials such as the "hydantoin hexacrylate" coatings described in U.S.Pat. No. 4,249,011 (Wendling), which is incorporated herein byreference, or other photopolymerizable multifunctional acrylates.

Although FIG. 7 illustrates the security control laminate on theinterior face of the glazing member (i.e., the face of the member whichis opposite to the face first exposed to the force of the impact), thelaminate may also be secured to the exterior face. Also contemplated isa glazing unit comprising multiple glazing members arranged in, forexample, a sandwich or an insulated construction wherein the securitycontrol laminate is secured to a face of a glazing member which isinterior to the sandwich or insulated construction. Additionally, it iscontemplated that the security control laminate may be adhesively ormechanically attached to a supplemental frame or batten system thatsurrounds the glazing member as well as to the glazing member itself. Aninstallation of this type provides additional security againstunintended removal or dislodgement of the glazing member from its framewhich would otherwise allow access through the glazing unit.

FIG. 8 illustrates a second embodiment of security control laminate 21which additionally includes a reflective metalized layer 30 to impartenergy control properties to the glazing unit. This embodiment issimilar to the security control laminate illustrated in FIG. 7 exceptthat metalized layer 30 is adjacent to multilayer film face 27b ratherthan abrasion resistant coating 28.

More particularly, a carrier film 31 supports metalized layer 30, thelatter being bonded to multilayer film face 27b by an adhesive layer 29.Metalized layer 30 may be aluminum, gold, silver, copper, nickel, or anyother suitable reflector of radiant energy over the solar and infraredspectrum (i.e., a wavelength of 0.3 to 40 μm). Metalized layer 30 may beapplied to carrier film 31 by, for example, vapor deposition.Preferably, metalized layer 30 is relatively transparent to visiblelight and offers good reflectivity of infrared radiation. Carrier film31 comprises an optically clear film, preferably an optically clearpolyester film, having a thickness in the range of about 13 to 51 μm(0.5 to 2.0 mils). Optionally, carrier film 31 may be dyed to provideadditional protection from radiation incident on the glazing unit. Inthis regard, any optical grade dyed film may be used. Such filmstypically comprise an optically clear polyester film which has beendipped in a heated solvent bath containing a dye of the desired (andoften customized) color, washed, rinsed and dried. Films of this typeare commercially available from Martin Processing Company (Martinsville,Va.). Adhesive layer 29 may be a laminating adhesive similar to adhesivelayer 26 for example. The embodiment of FIG. 8 may (but need not)include abrasion resistant coating 28 on the face of carrier film 31which does not support metalized layer 30.

FIG. 9 illustrates a third embodiment of security control laminate 21which utilizes a single multilayer film 25. The embodiment of FIG. 9 issimilar to those described in conjunction with FIGS. 7 and 8 with theexception that multilayer film 27 has been replaced by a dyed film 32that is secured to multilayer film face 25a by way of adhesive layer 26.Abrasion resistant coating 28 protects the opposite face of dyed film 32from mechanical abrasion. Dyed film 32 is similar to the dyed version ofcarrier film 31 described in conjunction with FIG. 8.

Constructions other than those illustrated above comprising differentarrangements of multilayer films, metalized films, and/or dyed films arealso possible. Such other constructions may offer various securityand/or solar control properties as will be appreciated by the skilledartisan. Furthermore, while certain coatings and layers may be describedherein as being "on" other coatings and layers of the security controllaminate, it will be understood that this encompasses both direct andindirect attachment to the other coatings or layers.

FIG. 10 illustrates the security control laminate of FIG. 8 beforeinstallation on a glazing member. Overcoat 33, which preferably is awater soluble material, is applied over adhesive layer 23 to protect itfrom damage during manufacture and handling. A variety of water solublematerials such as methyl cellulose or polyvinyl alcohol are suitable asthe overcoat material. Security control laminate 21 is temporarilydisposed on a removable release liner 34 which is discarded prior toinstallation of the laminate on the glazing member. Release linerstypically employed with solar control and security films may be used.The security control laminate is prepared for application by removingthe release liner and rinsing the laminate with water to remove overcoat33, thereby exposing and/or activating adhesive layer 23. Securitycontrol laminate 21 is then applied to the glazing member usingconventional installation techniques known in the art.

The following examples illustrate the particular utility of multilayerfilms according to the invention in providing security control laminatesfor glazing members. In these examples all parts and percentages are byweight and all film and layer thicknesses are nominal thicknesses.Single pane window glass panels having a security control laminateaccording to the invention applied to one face thereof were tested fortheir ability to withstand impact without puncture and/or tearing inaccordance with a modified version of American National StandardsInstitute's Specification for Safety Glazing Material Used in Buildings,ANSI Z97.1-1984. In general, tests were conducted by swinging a weightedshotbag into 0.3 cm and/or 0.6 cm thick glass panels in a pendulum arc,dropping the bag from heights of 45.7 cm (18 inches) and 122 cm (48inches). (The shotbag impacted the surface of the glass panel which didnot have the security control laminate bonded thereto.) The heights usedwill be recognized as corresponding to levels II and III of ANSIZ97.1-1984. The ANSI test setup was utilized but different numbers ofpanels were tested at less than all of the levels specified in thepublished procedure. An individual panel was considered to have met thetest requirements, if, after impact, a 7.6 cm diameter metal ballmounted on a rod could not be passed through any break in the panelresulting from the impact.

EXAMPLE 50

A multilayer film comprising 13 alternating layers of the stiff PET ofexamples 1 to 26 and the ductile copolyester of the same examples wascoextruded onto a chilled casting wheel and subsequently sequentiallyoriented 2.6 times in the machine direction at about 85° C. to 90° C.and 3.3 times in the transverse direction at 99° C. The resulting 58 μmthick film was heat set at 149° C. and comprised 7 wt. % of the ductilematerial.

One surface of the multilayer film was corona treated to a surfaceenergy of 40 to 44 dynes/cm under standard corona treating conditionsusing an apparatus available from Enercon Industries.

Adhesive was applied to the corona treated surface of the multilayerfilm by coating a 14.5% solids solution of a pressure sensitive adhesivecomprising 100 parts of a 96:4 isooctyl acrylate:acrylamide copolymer(prepared as described in U.S. Pat. No. Re. 24,906 to Ulrich, which isincorporated herein by reference), 2 parts of a UV absorber (UNIVULD-50, commercially available from BASF), 0.8 part of a fluorochemicalsurfactant (FC740, commercially available from Minnesota Mining andManufacturing Company), and 0.5 part of a substituted phenolic thioetherantioxidant (SANTINOX-R, commercially available from Monsanto Company)in a solvent system comprising 33 parts heptane, 32 parts ethyl acetate,29.5 parts toluene, and 6 parts methyl ethyl ketone. The coatedmultilayer film was then dried in a circulating air oven operating at105° C. for approximately 3 minutes to remove the solvent and to providea pressure sensitive adhesive having a dry coating weight of 22.6grams/square meter (g/m²). A 1.6% solids overcoat solution of METHOCELA15 LV (commercially available from Dow Chemical Co.) was applied overthe pressure-sensitive adhesive and the water was evaporated by passingthe coated film through a circulating air oven operating at 63° C. forapproximately 1 minute to provide a tack-free, water soluble coating of0.3 g/m² dry weight.

A 25 μm thick release liner comprising a release agent coated PET filmwas removably laminated to the METHOCEL coating by passing theconstruction through a pair of squeeze rolls to provide a securitycontrol laminate according the invention.

The release liner was removed, the film laminate was rinsed with waterto remove the METHOCEL coating, and the security control laminate wasapplied to both 0.3 cm thick and 0.6 cm thick clean glass panelsmeasuring 86.4 cm by 193 cm using standard installation techniques forsolar and security films. The resulting panels were dried at roomtemperature for six weeks before impact testing as previously described.Six panels (3 having a thickness of 0.3 cm and 3 having a thickness of0.6 cm) were tested at a drop height of 45.7 cm. All 6 panels met thetest requirements. When 4 panels (2 of each thickness) were tested atthe 122 cm drop height, none met the test requirements.

EXAMPLES 51 to 53

A series of security control laminates, each comprising two identicalmultilayer tear resistant films according to the invention, wasprepared. Each multilayer film was 51 μm thick and comprised 13alternating layers of the stiff PET of examples 1 to 26 and 5.6 wt. % ofthe ductile polymeric material of the same examples. The films werecoextruded onto a chilled casting wheel and were simultaneouslybiaxially oriented 3.3 times in each of the machine and transversedirection at 99° C. The multilayer films of examples 51 to 53 differedonly in the temperature at which they were heat set. The film of example51 was heat set at 149° C., the film of example 52 was heat set at 163°C., and the heat set temperature for the film of example 53 was 178° C.A toluene/methyl ethyl ketone (T/MEK) solution (3.7:1 weight to weightratio) of a tack free, polyester laminating adhesive was prepared bycombining 6% VITEL PE-307 (commercially available from GoodyearChemicals) and 0.3% MONDUR CB-75 (a curing agent available from MobayChemical Company). The solution was coated onto one of the multilayerfilms for each example and the coated films were dried in a circulatingair oven operating at 63° C. for approximately 2 minutes to provide dryadhesive coatings of approximately 0.8 g/m².

The second multilayer film for each example was laminated to theadhesive coated surface of the first multilayer film by passing thelayered structures through a pair of squeeze rollers operating at 75° C.and 207 dynes/cm² (30 psi). The dual film laminates were then coronatreated, coated with a pressure sensitive adhesive and overcoat, andprovided with a removable release liner, all as described more fully inexample 50.

The panels were prepared and tested for impact resistance as describedabove using 0.6 cm thick glass panels and a 122 cm drop height. Inexample 51, 8 of the 10 panels tested met the test requirements, while 5of the 10 panels did for example 52, and 4 of the 10 panels did forexample 53. Thus, examples 51 to 53 suggest that the performance ofsecurity control laminates according to the invention can be varied byappropriate selection of the temperature at which the multilayer film isheat set. For use in security control laminates, the multilayer films ofthe invention are preferably heat set at about 145° C. to 165° C., morepreferably about 149° C.

COMPARATIVE EXAMPLE 19

Comparative example 19 was a 102 μm thick commercially availablesecurity control film that comprised a pair of 51 μm thick biaxiallyoriented single layer PET films laminated together. Essentially, thesecurity control laminate of example 19 was like that of example 51except that it employed single layer PET films rather than themultilayer films of the invention. Comparative example 19 was testedaccording to the procedure of example 50. 6 panels (3 of each thickness)evaluated at the 45.7 cm drop height met the test requirements. Onepanel (0.3 cm thick glass) was tested at 122 cm and met the testrequirements.

EXAMPLE 54

A security control laminate is prepared according to the proceduredescribed in examples 51 to 53 with the exception that each multilayerfilm comprises 13 alternating layers of the stiff PET of example 27 to31 and 10 wt. % of the ductile material of the same examples. The filmis coextruded onto a chilled casting wheel, sequentially biaxiallyoriented 3.3 times in the machine direction at 99° C. and 3.4 times inthe transverse direction at 99° C., and heat set at 149° C.

EXAMPLE 55

The tack free, polyester laminating adhesive of examples 51 to 53 iscoated onto the multilayer film of example 51 and the coated film isdried in a circulating air oven operating 63° C. for approximately 2minutes to produce a dry adhesive coating of approximately 0.8 g/m². Asecond multilayer film of the same example is laminated to the adhesivecoated surface of the first multilayer film by passing the layeredstructure through a pair of squeeze rollers operating at 75° C. and 207dynes/cm² (30 psi) to provide a dual film laminate.

A 25 μm thick biaxially oriented PET carrier film is vapor coated withaluminum to a sheet resistance of approximately 9 ohms/square usingstandard vapor coating techniques. The visible spectrum transmission ofthe aluminum coated film is approximately 18% at a wavelength of 0.55μm. The tack free polyester laminating adhesive of example 51 is thencoated onto the aluminum surface of the PET carrier film and dried toprovide a dry adhesive coating of approximately 0.8 g/m². The resultingadhesive coated PET carrier film is then laminated to the uncoatedsurface of the dual film laminate by passing the layered structurethrough a pair of squeeze rollers operating at 75° C. and 207 dynes/cm²(30 psi).

The exposed surface of the carrier film is corona treated as describedin example 50 and a solution consisting of 100 parts hydantoinhexacrylate (HHA), 4 parts IRGACURE 184 (a photoinitiator commerciallyavailable from Ciba-Geigy Corporation), and 418 parts MEK is immediatelycoated onto the corona treated surface. The coated construction is thenpassed through a circulating air oven operating at 49° C. forapproximately 3 minutes to provide an HHA coating of approximately 2.7g/m². The HHA coating is then cured by passing the construction underthree banks of 200 watts/inch medium pressure mercury vapor UV lamps ata line speed of 30.5 meters/minute (100 feet/minute) and a lamp to filmdistance of 12 cm to provide an abrasion resistant coating.

A UV absorbent composition is prepared by combining 7.5 parts of asubstituted benzophenone (e.g., UVINUL M-493 or UVINUL D-50,commercially available from BASF), 92.5 parts VITEL PE-222 (a PETterpolymer commercially available from Goodyear Chemicals), and asufficient volume of a 1:1 weight to weight ratio T/MEK solvent systemto produce a 26% solids solution.

The uncoated surface of the multilayer film laminate is corona treatedto a surface energy of 40 to 44 dynes/cm (using an apparatus availablefrom Enercon Industries) and the above described UV absorbingcomposition is immediately coated onto the corona treated surface. Thecoated laminate is then passed through a circulating air oven operatingat 65° C. for approximately 2 minutes to provide a UV absorbent layerhaving a dry coating weight of 5.4 g/m². A pressure sensitive adhesivelayer is coated over the UV absorbing composition according to example50 (where it was applied directly to the corona treated surface) to adry coating weight of 22.6 g/m². The adhesive layer is then overcoatedwith a tack-free, water activatable METHOCEL layer. A 25 μm thickrelease liner (such as used in example 50) is removably laminated to theMETHOCEL coating by passing them through a pair of squeeze rolls.

EXAMPLE 56

Example 56 is similar to example 55 except that the aluminum vaporcoated PET carrier film is replaced with a dyed PET film such as anoptically clear dyed film commercially available from Martin ProcessingCompany (Martinsville, Va.) that is laminated to the dual filmconstruction.

Reasonable variations and modifications are possible within the scope ofthe foregoing specification and drawings without departing from theinvention which is defined in the accompanying claims.

The embodiments for which an exclusive property or privilege is claimedare defined as follows:
 1. A security control laminate comprising afirst tear resistant film having a first face and a second face oppositethe first face and a first layer of adhesive on the first face of thetear resistant film for bonding the security control laminate to asurface, the first tear resistant film comprising a total of more thanfive stiff and ductile layers situated one on the other in a parallelarray, the layers occurring essentially randomly in the array, wherein(a) at least two of the layers are a stiff polyester or copolyester thathas a tensile modulus greater than 200 kpsi, the layers of stiffpolyester or copolyester having an average nominal thickness greaterthan about 1 μm, and (b) at least two other layers are a ductilepolymeric material that has been oriented in at least one direction, hasa tensile modulus less than 200 kpsi, and has a tensile elongationgreater than 50%.
 2. A security control laminate according to claim 1further comprising means for absorbing ultraviolet radiation, the meansbeing either on or incorporated into a layer of the security controllaminate.
 3. A security control laminate according to claim 2 whereinthe means for absorbing ultraviolet radiation is a coating layerinterposed between the first tear resistant film and the first layer ofadhesive.
 4. A security control laminate according to claim 1 furthercomprising a dyed film, a surface of which is adhesively bonded to thesecond face of the first tear resistant film.
 5. A security controllaminate according to claim 4 further comprising an abrasion resistantcoating on a surface of the dyed film opposite the surface which isadhesively bonded to the tear resistant film.
 6. A security controllaminate according to claim 1 further comprising a second tear resistantfilm, one face of which is adhesively bonded to the second face of thefirst tear resistant film, the second tear resistant film comprising atotal of more than five stiff and ductile layers situated one on theother in a parallel array, the layers occurring essentially randomly inthe array, wherein (a) at least two of the layers are a stiff polyesteror copolyester that has a tensile modulus greater than 200 kpsi and (b)at least two other layers are a ductile polymeric material that has beenoriented in at least one direction, has a tensile modulus less than 200kpsi, and has a tensile elongation greater than 50%.
 7. A securitycontrol laminate according to claim 6 further comprising a metallizedlayer on either the first or the second tear resistant film.
 8. Asecurity control laminate according to claim 7 wherein the metallizedlayer is secured to a face of the second tear resistant film oppositethe face which is bonded to the first tear resistant film.
 9. A securitycontrol laminate according to claim 7 wherein the metallized layercomprises an optically clear film having a layer of metal selected fromthe group consisting of aluminum, gold, silver, nickel and copperthereon.
 10. A security control laminate according to claim 7 furthercomprising an abrasion resistant coating over the metallized layer. 11.A security control laminate according to claim 1 wherein the layers ofstiff polyester or copolyester and the layers of ductile polymericmaterial have been biaxially oriented.
 12. A security control laminateaccording to claim 1 wherein the first tear resistant film has a Gravesarea in one direction of the film equal to at least 40+0.4(x) kpsi %,wherein x is the nominal thickness of the first tear resistant film inmicrons.
 13. A security control laminate according to claim 12 whereinthe first tear resistant film has a tensile modulus of at least 175 kpsiin one direction of the film.
 14. A security control laminate accordingto claim 13 wherein the first tear resistant film has a tensile modulusof at least 450 kpsi in one direction of the film.
 15. A securitycontrol laminate according to claim 12 wherein the first tear resistantfilm has a Graves elongation at break of at least 20% in the teardirection of the film measured during the determination of Graves area.16. A security control laminate according to claim 15 wherein the firsttear resistant film has a Graves elongation at break of at least 40% inthe tear direction of the film measured during the determination ofGraves area.
 17. A security control laminate according to claim 1wherein the stiff polyester or copolyester comprises the reactionproduction of (a) a dicarboxylic acid component selected from the groupconsisting of terephthalic acid, naphthalene dicarboxylic acid and esterderivatives thereof, and (b) a diol component selected from the groupconsisting of ethylene glycol and 1,4-butanediol.
 18. A security controllaminate according to claim 1 wherein the ductile polymeric material isselected from the group consisting of ethylene copolymers, polyesters,copolyesters, polyolefins, polyamides, and polyurethanes.
 19. A securitycontrol laminate according to claim 18 wherein the ductile polymericmaterial is a copolyester comprising the reaction product of cyclohexanedicarboxylic acid (or ester derivatives thereof), cyclohexane dimethanoland polytetramethylene glycol.
 20. A security control laminate accordingto claim 1 wherein the ductile polymeric material provides at most about20 weight percent of the first tear resistant film.
 21. A securitycontrol laminate according to claim 1 further comprising a layer of anintermediate material disposed between otherwise adjacent layers ofstiff polyester or copolyester and ductile polymeric material whereinthe layer of intermediate material enhances the adhesion between theotherwise adjacent layers of stiff polyester or copolyester and ductilepolymeric material.
 22. A security control laminate comprising a firsttear resistant film having a first face and a second face opposite thefirst face and a first layer of adhesive on the first face of the tearresistant film for bonding the security control laminate to a surface,the first tear resistant film comprising a total of more than five stiffand ductile layers situated one on the other in a parallel array, thelayers occurring essentially randomly in the array, wherein (a) at leasttwo of the layers are a stiff polyester or copolyester that has atensile modulus greater than 200 kpsi, the layers of stiff polyester orcopolyester having an average nominal thickness of about 1 to 15 μm, and(b) at least two other layers are a ductile polymeric material that hasa tensile modulus less than 200 kpsi and a tensile elongation greaterthan 50%, wherein the ductile polymeric material is selected from thegroup consisting of ethylene copolymers, polyesters, copolyesters,polyolefins, and polyamides.
 23. A security control laminate accordingto claim 22 further comprising means for absorbing ultravioletradiation, the means being either on or incorporated into a layer of thesecurity control laminate.
 24. A security control laminate according toclaim 22 further comprising a dyed film, a surface of which isadhesively bonded to the second face of the first tear resistant film.25. A security control laminate according to claim 24 further comprisingan abrasion resistant coating on a surface of the dyed film opposite thesurface which is adhesively bonded to the first tear resistant film. 26.A security control laminate according to claim 22 further comprising asecond tear resistant film one face of which is adhesively bonded to thesecond face of the first tear resistant film, the second tear resistantfilm comprising a total of more than five stiff and ductile layerssituated one on the other in a parallel array, the layers occurringessentially randomly in the array, wherein (a) at least two of thelayers are a stiff polyester or copolyester that has a tensile modulusgreater than 200 kpsi and (b) at least two other layers are a ductilepolymeric material that has a tensile modulus less than 200 kpsi and atensile elongation greater than 50%.
 27. A security control laminateaccording to claim 26 further comprising a metallized layer on the faceof the second tear resistant film opposite the face which is bonded tothe first tear resistant film.
 28. A security control laminate accordingto claim 27 further comprising an abrasion resistant coating over themetallized layer.
 29. A security control laminate according to claim 22wherein the first tear resistant film has a Graves area in one directionof the film equal to at least about 40+0.4(x) kpsi %, wherein x is thenominal thickness of the first tear resistant film in microns.
 30. Asecurity control laminate according to claim 29 wherein the first tearresistant film has a tensile modulus of at least 175 kpsi in onedirection of the film.
 31. A security control laminate according toclaim 30 wherein the first tear resistant film has a tensile modulus ofat least 450 kpsi in one-direction of the film.
 32. A security controllaminate according to claim 29 wherein the first tear resistant film hasa Graves elongation at break of at least 20% in the tear direction ofthe film measured during the determination of Graves area.
 33. Asecurity control laminate according to claim 32 wherein the first tearresistant film has a Graves elongation at break of at least 40% in thetear direction of the film measured during the determination of Gravesarea.
 34. A security control laminate comprising a tear resistant filmhaving a first face and a second face opposite the first face and afirst layer of adhesive on the first face of the tear resistant film forbonding the security control laminate to a surface, the tear resistantfilm comprising a total of more than five stiff and ductile layerssituated one on the other in a parallel array, the layers occurringessentially randomly in the array, wherein (a) at least two of thelayers are a stiff polyester or copolyester that has a tensile modulusgreater than 200 kpsi, the layers of stiff polyester or copolyesterhaving an average nominal thickness of about 1 to 15 μm, and (b) atleast two other layers are a ductile polymeric material that has atensile modulus less than 200 kpsi and a tensile elongation greater than50%, the layers of ductile polymeric material having an average nominalthickness of less than 3 μm.
 35. A security control laminate accordingto claim 34 wherein the tear resistant film has a Graves area in onedirection of the film equal to at least about 40+0.4(x) kpsi %, whereinx is the nominal thickness of the first tear resistant film in microns.36. A security control laminate according to claim 35 wherein the tearresistant film has a tensile modulus of at least 175 kpsi in onedirection of the film.
 37. A security control laminate according toclaim 36 wherein the tear resistant film has a tensile modulus of atleast 450 kpsi in one direction of the film.
 38. A security controllaminate according to claim 34 wherein the tear resistant film has aGraves elongation at break of at least 20% in the tear direction of thefilm measured during the determination of Graves area.
 39. A securitycontrol laminate according to claim 38 wherein the tear resistant filmhas a Graves elongation at break of at least 40% in the tear directionof the film measured during the determination of Graves area.
 40. Asecurity control laminate according to claim 34 further comprising meansfor absorbing ultraviolet radiation, the means being either on orincorporated into a layer of the security control laminate.
 41. Asecurity control laminate according to claim 40 further comprising adyed film, a surface of which is adhesively bonded to the second face ofthe tear resistant film.
 42. A security control laminate according toclaim 41 further comprising an abrasion resistant coating on a surfaceof the dyed film opposite the surface which is adhesively bonded to thetear resistant film.
 43. A security control laminate comprising:(A) atear resistant film having a first face and a second face opposite thefirst face; (B) a first layer of adhesive on the first face of the tearresistant film for bonding the security control laminate to a surface;and (C) means for absorbing ultraviolet radiation, the means beingeither on or incorporated into a layer of the security control laminate;wherein the tear resistant film comprises a total of about thirteenalternating stiff and ductile layers situated one on the other in aparallel array, and further wherein:(a) about seven of the layers are astiff polyester or copolyester that has a tensile modulus greater than200 kpsi and that comprises the reaction product of (i) a dicarboxylicacid component selected from the group consisting of terephthalic acid,naphthalene dicarboxylic acid, and ester derivatives thereof, and (ii) adiol component selected from the group consisting of ethylene glycol and1,4-butanediol, the layers of stiff polyester or copolyester having anaverage nominal thickness greater than about 1 μm; (b) about six otherlayers are a ductile polymeric material that has a tensile modulus lessthan 200 kpsi and a tensile elongation greater than 50%; (c) the tearresistant film has a Graves area in one direction of the film equal toat least about 40+0.4(x) kpsi %, wherein x is the nominal thickness ofthe tear resistant film in microns; (d) the tear resistant film has aGraves elongation at break of at least 20% in the tear direction of thefilm measured during the determination of Graves area; and (e) the tearresistant film has a tensile modulus of at least 175 kpsi in onedirection of the film.